1. Field of Invention
The present invention relates to a method of monitoring blood flow in a blood vessel by employing ultrasonic Doppler technology and more specifically, it involves such a method which is advantageously employable in monitoring blood flow after microvascular surgery.
2. Description of the Prior Art
It has been known in connection with the monitoring of blood vessels after microvascular surgery to employ an ultrasonic Doppler probe which may take the form of a sleeve to which an ultrasonic transducer has been secured. After completion of monitoring, the probe and supporting sleeve must be surgically removed. See generally Swartz at al. "Direct Monitoring of Microvascular Anastomose with the 20-Mhz Ultrasonic Doppler Probe: An Experimental and Clinical Study," Plastic and Reconstructive Surgery, pages 149-158 (February 1988). See also Pinnella et al. "Direct Microvascular Monitoring with Implantable Ultrasonic Doppler Probes," Journal of Microsurgery, pages 217-221 (Summer 1982) and Bandyk et al. "Detection of Technical Error During Arterial Surgery by Pulsed Doppler Spectral Analysis," Arch. Surg. Volume 119, pages 421-428 (April 1984). It has also been known to employ implanted cuffs around nerves in order to stimulate nerve activity artificially or dampen nerve activity, or to deliver medication. See generally U.S. Pat. Nos. 4,602,624; 4,628,942; 4,649,936; and 5,092,332.
It is of great importance after microvascular surgery to monitor the region of the surgery in order to make sure that the blood flow is maintained at the desired level and that no problems, such as thromboses have occurred. Should thrombosis occur, the transferred tissue would die. Conventional techniques employ transcutaneous methods such as ultrasonic Doppler or laser Doppler. It has also been known to employ experimental sleeves which along with the wire and ultrasonic transducer must be surgically removed after completion of the monitoring period. Such monitoring is particularly important where the microvascular surgery has been performed on a blood vessel which is spaced below the skin surface.
It has been known to employ indirect means of monitoring the functioning of blood flow through blood vessels which have been subjected to microvascular surgery. For example, surface temperature measurements, transcutaneous PO.sub.2 monitoring, photoplethysmography and laser Doppler flow meters have been employed. These approaches generally require an accessible exposed portion of the flap. Buried free tissue transfers and intraoral flaps cannot be monitored effectively by these methods.
It has also been known to employ an implantable thermocouple device which can be used without the need for exposed surface contact with the flap, but in general, this approach has been deemed inadequate and use has by and large has been discontinued. See generally, May et al. "Removable Thermocouple Probe Microvascular Patency Monitor: An Experimental and Clinical Study," Plast. Reconstr. Surg. 72:366 1983.
In spite of the foregoing known approaches there remains a substantial need for an improved means for monitoring blood flow within a patient.